Evaporation of fuel which leaks into the atmosphere from a fuel tank, a float chamber of a carburetor, etc. is one of the causes of air pollution and results in loss of fuel. Various techniques are known for preventing this problem from occurring. As one typical means for obviating such problem, there is an evaporation system in which evaporated fuel generated in a fuel tank, etc. is temporarily absorbed and retained in a canister having an absorbent therein, and the evaporated fuel absorbed and retained in this canister is purged and discharged so as to be supplied to the engine during the operation thereof.
One example of the evaporation fuel control apparatus for an engine of the type mentioned above is disclosed in Japanese Patent Early Laid-Open Publication No. Hei 2-130254. The evaporation fuel control apparatus disclosed in this Publication comprises a communication passage for intercommunicating a fuel tank and a canister, a stop valve for opening and closing this communication passage, and stop detection means for detecting the stopping of the engine or the stopping of the vehicle, drive means for opening the stop valve for a predetermined period of time from the time when the stopping of the engine or the stopping of the vehicle is detected, the stop valve being opened for a predetermined period of time, and evaporated fuel contained in the fuel tank being guided to the canister so as to be retained, thereby extensively restraining the amount of the evaporated fuel from being discharged to the atmospheric air from a fuel tank feed port even when a filler cap is opened during filling of the fuel tank.
An example of a conventional evaporation fuel control apparatus for an engine is shown in FIG. 1. In FIG. 1, the numeral 202 denotes an engine, 204 an air cleaner, 206 a throttle valve, 208 a surge tank, 210 an inlet passage, 212 a combustion chamber, 214 a discharge passage, and 216 a fuel tank, respectively. An evaporation fuel control apparatus 218 for the engine 202 comprises an air passage 220 which is communicated at one end thereof with the surge tank 208 associated with the inlet passage 210 of the engine 202, the other end of the air passage 220 being communicated with the fuel tank 216.
A canister 222 is disposed at an intermediate part of the air passage 220, the canister 222 being adapted for absorbing and retaining evaporated fuel therein. A stop valve 224 is disposed at an intermediate part of the air passage 220 for intercommunicating the canister 222 and the surge tank 208. This stop valve 224 is opened and closed by a control unit (not shown) so that the evaporated fuel absorbed and retained in the canister 222 can be removed and discharged from the canister 222 so as to be supplied to the combustion chamber 212 in accordance with an operating condition of the engine 202. Furthermore, a check valve 226 is disposed at an intermediate part of the air passage 220 for intercommunicating the canister 222 and the fuel tank 216. This check valve 226 is opened when the internal pressure of the fuel tank 216 is brought to be equal to or greater than a set pressure.
In the evaporation fuel control apparatus 218 thus constructed, heretofore, the check valve 226, which is operated to open when the internal pressure of the fuel tank 216 is equal to or greater than a set pressure higher than that of the atmospheric air, is provided taking into consideration an excessive filling of fuel into the fuel tank 216 during filling thereof, so that the internal pressure of the fuel tank 216 can be controlled to the set pressure. Owing to this arrangement, the internal pressure of the fuel tank 216 accumulates to the set pressure.
Therefore, for the supply of fuel to the fuel tank 216, when a fuel feed cap 232 is removed from a fuel feed port 230 of a fuel feed passage 228, the internal pressure of the fuel tank 216 accumulated at the set pressure is released, with the unfavorable result that the evaporated fuel is discharged into the atmosphere.
In an evaporation restriction anticipated to be employed from 1995 model year vehicles in the United States, the internal pressure of the fuel tank is restricted to a predetermined level, for example, 10 inch mm Ag or less, during the operation of the engine. Therefore, an evaporation fuel control apparatus for an engine which is capable of coping with this evaporation restriction is keenly demanded.
In order to obviate this inconvenience, there is known another device in which the internal pressure of the fuel tank 216 is controlled to be equal to or less than a predetermined pressure (for example, 10 inch mm Ag or lower), which is lower than the set pressure of the check valve 226, during the operation of the engine 202. However, if the set pressure obtained by opening the check valve 226 is set to a low level in order to control the internal pressure of the fuel tank 216 so as to be equal to or lower than the predetermined pressure, it gives rise to such inconvenience that the check valve 226 is opened during the supply of fuel to the fuel tank 216, with the result that an excessive filling of the fuel into the tank cannot be prevented.
According to one embodiment of the present invention, in order to obviate the above inconveniences, there is provided an evaporation fuel control apparatus for an engine comprising a canister disposed at an intermediate part of a passage for intercommunicating an inlet passage of an engine and a fuel tank, and adapted to draw and retain evaporated fuel, characterized by further comprising a first control passage for intercommunicating the fuel tank and the canister, a second control passage for intercommunicating the canister and the inlet passage, a pressure valve disposed at an intermediate part of the first passage, a first solenoid valve being provided at an intermediate part of the second passage, a communication passage for intercommunicating the inlet passage and the pressure control valve, a second solenoid valve disposed at an intermediate part of the communication passage, a fuel detection device such as a level gauge associated with the fuel tank and adapted to detect an amount of fuel, and a control for controlling the second solenoid valve so that the inlet pipe negative pressure acts on and opens the pressure control valve during operation of the engine, and the atmospheric air pressure acts on and closes the pressure control valve in accordance with a detection signal coming from the fuel detection device when the fuel level or internal pressure in the fuel tank is brought equal to or more than a predetermined amount.
By virtue of the embodiment of the invention thus constructed, during operation of engine, the negative pressure in the inlet passage acts on the pressure control valve through the second solenoid valve, and the pressure control valve is opened to bring the internal pressure of the fuel tank generally equal to the atmospheric air pressure. When the fuel in the fuel tank is brought equal to or more than a predetermined amount, the second solenoid valve is operated in accordance with the detection signal so as to cause the atmospheric air to act on the pressure control valve in order to cut off the communication between the fuel tank and the canister, thereby preventing an excessive filling of fuel when the tank is supplied with fuel.
According to another embodiment of the present invention, there is provided, in order to obviate the above inconveniences, an evaporation fuel control apparatus for an engine wherein an air passage is communicated at one end thereof with an inlet passage of an engine, the other end of the air passage being bifurcated into a first branch air passage and a second branch air passage, the first and second branch air passages being communicated with a fuel tank, a canister being disposed at an intermediate part of the air passage and adapted to draw and retain evaporated fuel, a stop valve being disposed at an intermediate part of the air passage between the canister and the inlet passage, a check valve being disposed at an intermediate part of the first branch air passage, the check valve being opened when pressure within the fuel tank is brought to be equal to or more than a predetermined set pressure, a control valve being disposed at an intermediate part of the second branch air passage, the control valve being opened during operation of the engine, a float valve being disposed at an opening within the fuel tank of the first branch air passage, the float valve being closed when the fuel tank is fully filled with fuel.
According to the present invention constructed according to this latter embodiment, since the control valve is opened to communicate the second branch air passage during the operation of the engine, the internal pressure of the fuel tank can be brought generally to the atmospheric air pressure. As a result, since the fuel is supplied to the fuel tank immediately after the stoppage of the engine, the internal pressure of the fuel tank is already generally equal to the atmospheric air pressure. When the fuel tank is filled with fuel as a result of the supply of fuel thereto, the float valve is closed. The fuel tank is fully filled with fuel with only an upper space thereof left vacant, and the further supply of the fuel to the tank is interrupted. As a result, the internal pressure of the fuel tank is kept controlled to be the set pressure as determined by the check valve. Furthermore, since the internal pressure of the fuel tank is already made generally equal to the atmospheric air pressure, fuel can be supplied to the tank even during operation of the engine.